A method of making a mandrel of a blind rivet

Abstract: A metal rod having a conical or pyramidal cut extremity is used to make a mandrel (21) of a blind rivet. The rod is held in place between a pair of die segments (11) such that an end of a preset length including the cut extremity is swageable and protrudes from an upper surface (14) of the segments (11). Subsequently, the swageable end (26) is axially compressed to form a mandrel head (27) by a punch (12) which has a lower face (17) extending parallel to the upper surface (14) of the segments (11) and a conical or pyramidal recess (18) fittable on the cut extremity. Thus, a free intermediate portion of the swageable end (26) compressed by the punch (12) swells radially to form the head (27) which has a flat flange (31) from which the cut extremity (20a) protrudes as a lug (32) upwardly and centrally. The mandrel (21), which has the head formed uniform without any eccentricity about the axis of a mandrel body, can thus be produced inexpensively using nail manufacturing apparatus.

Description: The invention relates to a method of making a mandrel of a blind rivet. Figures 7(a) and 7(b) of the accompanying drawings show a typical example of prior art blind rivets. A blind rivet 1 comprises a cylindrical rivet body 2 and a mandrel 5 inserted therein, the rivet body having at one end thereof a flange-shaped rivet head 3. A bore 4 through the rivet body receives the mandrel 5, which comprises a mandrel body 5 a having at its end a mandrel head 6. Adjacent the mandrel head is a constricted portion 7 in the mandrel body 5 a . The mandrel head 6 and the constricted portion 7 are located opposite to the rivet 3 located at the other, open end 2 a of the rivet body 2. The mandrel head 6 can, in use, plastically deform and expand the other, open end 2 a of the rivet body. The mandrel body 5 a will subsequently be broken off the mandrel head 6, at the constricted portion 7. The reference numerals 8 and 9 denote two workpieces to be fastened one to the other (see for example FR-A-1 096 383). Such mandrels 5 for the blind rivets 1 are made of a metal rod, for example of an iron rod inexpensively by using in general a nail manufacturing apparatus. The round mandrel heads 6 are formed in a one-shot manner by a punching press, directly without performing any preliminary pressing step. It is however noted that the iron rods severed in the nail manufacturing apparatus generally have their extremities wedge-shaped or pyramid-shaped. Usually, those iron rods having such extremities are directly pressed in a spherical cavity of the punching press, in a state such that their ends protrude a comparatively great distance from a split die. Those ends tend often to slant noticeably or swell irregularly in radial direction during the pressing process, so that the pressed heads 6 are rendered somewhat offset with respect to the axes of the mandrel bodies 5 a . Thus, a peripheral portion of the mandrel head is likely to be uneven in its thickness and/or shape around the axis of each mandrel body. If, in use, such an irregularly formed head 6 of the mandrel 5 presses or expands the open end 2 a of the rivet body 2, then the open end 2 a will be deformed non-uniformly as shown in Figure 7(b). Consequently, the mandrel head 6 will tend to slip off the rivet body, or the rivet body 2 will collapse during the riveting operation, and/or the rivet as a whole will fail to ensure an expected strength of connection, due to such an irregular deformation. According to the invention there is provided a method of making a mandrel of a blind rivet), comprising the steps of: preparing as the starting material of the mandrel a metal rod produced in nail manufacturing apparatus and having a pointed cut extremity formed by means of a pair of severing blades of said apparatus; holding the metal rod in place between a pair of split die segments, in such a state that the metal rod has a swageable end of a predetermined length including the cut extremity protruding from an upper surface of the split die; and pressing the swageable end in its axial direction by means of a punch so that a head is formed on the mandrel from the swageable end and integral with the rod; wherein the punch has a substantially flat lower face and a recess formed therein to be of a dimension and shape complementary to said pointed cut extremity of the method rod; and wherein the punch compresses the swageable end of the rod having the cut extremity fitted in the recess such that the swageable end is caused to swell radially and evenly to form the head comprising a flat flange from which the pointed cut extremity protrudes upwardly and centrally thereof. Such a method can ensure that a swageable end of a metal rod, for example an iron rod, can be compressed axially to swell evenly in the radial direction so as not to cause any eccentricity with respect to its axis or its thickness therearound, though the mandrel can be manufactured inexpensively in any conventional nail manufacturing apparatus. The recess in the punch used in this method is preferably formed to become narrower towards its inner region. In the method outlined above, the swageable end of the predetermined length and including the cut extremity is firmly gripped at both its longitudinal ends by the split die segments and the punch recess while being pressed in axial direction to form the head. Therefore, the swageable end will neither slant nor irregularly collapse, but will swell uniformly in radial direction. The head thus formed has an axis in alignment with the axis of a mandrel body, and is free from any irregular radius about its axis. The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which: Figure 1 is a front elevation of relevant parts of an apparatus to carry out a method of making a mandrel of a blind rivet according to the invention, with the parts shown in cross-section; Figure 2 is a view similar to Figure 1 showing an intermediate step of the method, wherein an iron rod is being pressed to form a head integral with the mandrel; Figure 3 is a view similar to Figures 1 and 2 showing a final step of the method, wherein the pressing of the iron rod is finished to provide the head with a flange; Figure 4 is a front elevation of a blind rivet comprising the mandrel and a rivet body shown in cross section, with the mandrel having been prepared as shown in Figures 1 to 3; Figure 5 also is a front elevation the blind rivet of Figure 4 after setting in use; Figure 6 shows a final step of the method in another embodiment, wherein the pressing is finished to provide a mandrel having a similar head; Figure 7(a) is a cross section of a prior art blind rivet, in a state before being set; and Figure 7(b) is a similar cross section view to Figure 7(a) of a prior art blind rivet, in a state after being set. Figures 1 to 3 illustrate sequential steps carried out in a mandrel manufacturing apparatus 10 to perform the method proposed herein. This apparatus 10 may be incorporated in a nail manufacturing machine of conventional kind. The mandrel manufacturing apparatus 10 comprises a split die which is composed of a pair of segments 11 and 11. The segments 11 have surfaces facing one another, and each of them has a groove 13 semicircular in cross section. A metal rod 20 comprising the starting material of the mandrel 21 to be produced will be gripped by and between the semi-cylindrical grooves 13. An upper surface 14 of each split die segment 11 is flat and extends perpendicular to the axis of the grooves 13. Each groove in the die segments has a gentle rise 15 and a sharp ridge 16, and the rises 15 are of a shape such that shallow recesses 24 will be formed in a body 22 of the mandrel 21. Bulges 23 will thus be produced each between the shallow recesses 24 so as temporarily to hold the mandrel body 22 in a rivet body 41 (see Figure 4). The sharp ridges 16 will make deep recesses 25 in the mandrel body 22, so that they serve as a breaking point where the lower portion of the mandrel body is torn off the upper portion, in use and after the rivet has been set. In operation, the die segments 11 will be forced at first to take their position closest to each other so that their gentle rises 15 and sharp ridges 16 grip the metal rod 20 and deform it to have the shallow and deep recesses 24 and 25, respectively, before forming of a head of the mandrel. A cut extremity 20 a of the metal rod 20 is diamond-shaped due to the severing thereof in the nail manufacturing apparatus. The one end of each metal rod 20 is seized at such a cut extremity 20 a . Alternatively, the cut extremity 20 a may be of a conical shape, which also may be produced easily and similarly by the severing of a metal rod in the nail manufacturing apparatus. On the other hand, a punch 12 has a lower face 17 flat and in parallel with the upper surfaces 14 of the die segments 11. A pyramid shaped recess 18 is present centrally of the punch and an in alignment with the pyramid-shaped cut extremity 20 a of the metal rod 20. The metal rod 20 has a swageable end 26 of a length 'L' protruding from the upper surfaces 14, with this end 26 being integral with and extending from the body 22 of the rod to form the mandrel 21 which is fixed in place by and between the die segments 11 and 11. The punch 12 will compress in the axial direction the swageable end 26 to form a head 27 (see Figure 3) while the cut extremity 20 a is retained in the recess 18 of the punch 12. In detail, a main portion of the swageable end 26, that is to say exclusive of the cut extremity 20 a , will swell at first in a radial direction as shown in Figure 2. The lower face 17 of the punch 12 will further press the swelled portion towards the upper surfaces 14 of the die segments 11, until a flange 31 is formed from the swelled portion. As shown in Figure 3, the flange 31 has a smooth and convex periphery 28 defined between an upper and lower faces 29 and 30 respectively, wherein the periphery is produced spontaneously so as to bulge outwardly at its middle height. A lug 32 originating from the pyramidal extremity 20 a will protrude upward from the flange 31 of the thus produced head 27 of the mandrel 21. During the swaging by the punch 12, both the longitudinal end portions of the swageable end 26 are restrained to keep their positions in alignment with each other, but an intermediate portion of the swageable end 26 is not restrained but allowed to deform in radial direction. Therefore, the swageable end 26 does neither slant nor bend itself, but will bulge uniformly in radial direction to provide the head 27 which is free from any eccentricity in its axis or in its radius therearound. Figure 4 shows a blind rivet 40 comprising the mandrel 21 manufactured in the described manner and incorporated in a rivet body 41. Figure 5 illustrates the blind rivet 40 in use, wherein the rivet body 41 has at its end a flange-shaped head 42 of known kind. The rivet body 41, made for example of a soft metal such as an aluminium alloy, is of a cylindrical shape and has an axial bore 43 to receive the mandrel. Figure 6 shows a modified apparatus for carrying out the method of the invention. This apparatus comprises die segments 11 which have in their upper surfaces shallow recesses 19. The recesses 19 will restrict to some extent the radial expansion of the swageable end 26, particularly of a lower peripheral portion of the flange 31. Such a partial restriction is effective to produce a mandrel head 27 with improved accuracy in the dimensions of its lower periphery. In summary, the swageable end of a predetermined length and including the cut extremity formed by the severing of an iron rod in the nail manufacturing machine is firmly and surely gripped at both its longitudinal end portions while being pressed in axial direction to produce the head by the radial expansion of an unrestrained intermediate portion of the rod. The pair of die segments cooperate with the punch having the recess of a shape fittable on the extremity so as to ensure such a temporary retention of the metal rod. Therefore, the swageable end will neither slant nor irregularly collapse, but will swell uniformly in radial direction, so that the mandrel head thus formed has an axis in alignment with the axis of a mandrel body, and is free from any irregular radius about its axis. Any blind rivet which comprises such a mandrel having the described head can be deformed uniformly in the riveting operation, thereby ensuring a reliable fastening of workpieces which are to be fastened one to another with an invariable strength.

Claims: A method of making a mandrel (21) of a blind rivet (40), comprising the steps of: preparing as the starting material of the mandrel a metal rod (20) produced in nail manufacturing apparatus and having a pointed cut extremity (20 a ) formed by means of a pair of severing blades of said apparatus; holding the metal rod (20) in place between a pair of split die segments (11), in such a state that the metal rod (20) has a swageable end (26) of a predetermined length including the cut extremity (20 a ) protruding from an upper surface (14) of the split die (11); and pressing the swageable end (26) in its axial direction by means of a punch (12) so that a head (27) is formed on the mandrel (20) from the swageable end (26) and integral with the rod (20); wherein the punch (12) has a substantially flat lower face (17) and a recess (18) formed therein to be of a dimension and shape complementary to said pointed cut extremity (20 a ) of the metal rod (20); and wherein the punch (12) compresses the swageable end (26) of the rod (20) having the cut extremity (20 a ) fitted in the recess (18) such that the swageable end (26) is caused to swell radially and evenly to form the head (27) comprising a flat flange (31) from which the pointed cut extremity (20 a ) protrudes upwardly and centrally thereof. A method according to claim 1, wherein the recess (18) in the punch (12) is formed to become narrower towards its inner region. A method according to claim 1 or claim 2, wherein the die segments (11) have in their upper surfaces (14) shallow recesses (19) to restrict the radial expansion of the swageable end (26), particularly of a lower peripheral portion of the flange (31) formed therein.

Inventors: SHINJO KATSUMI, SHINJO, KATSUMI
Applicants: SHINJO SEISAKUSHO YK, YUGENKAISHA SHINJO SEISAKUSHO
Application year: 1994
Main classification: B21K1
IPC codes: F16B19, B21F5, B21J15, B21G3, B21K1